The diffusion transfer photographic method utilizing silver salts, such as silver halide, is well known. In one technique for practicing such a photographic method, a light-sensitive element containing an exposed silver halide photographic emulsion and an image-receiving element containing silver-precipitating nuclei are superposed, and then an alkaline processing solution containing a silver halide solvent is introduced in between the above two elements to process them in the presence of a developing agent, thereby forming a positive silver image directly on the image-receiving element.
In the above method, the portion of the silver halide emulsion which, after exposure, remains unexposed in the light-sensitive element is dissolved by the silver halide solvent and eluted in the alkaline processing solution as a silver ion complex. This silver ion complex is transferred to the image-receiving element and precipitates therein as a silver image under the action of silver-precipitating nuclei. In this way, a positive image is formed directly on the image-receiving element.
In this method, however, a problem arises in that the silver image formed in the image-receiving element is liable to discolor or fade during its storage.
In order to overcome the above problem, Japanese Patent Publication No. 5392/71, U.S. Pat. No. 3,533,789 and British Pat. No. 1,164,642 disclose a method in which the surface of the silver image is coated with a water-soluble polymer solution containing an alkali-neutralizing component. This method, however, has disadvantages in that it takes a considerably long time for the surface coated with the aqueous polymer solution to become completely dry; since the surface is sticky and adhesive until it becomes completely dry, a print cannot be superposed thereon and finger prints or dust often attach thereto. This method also has the disadvantage that it is troublesome to further coat the silver image with such a solution.
Japanese Patent Publication No. 44418/81 discloses an image-receiving element comprising a support and the following layers: (1) a cellulose ester, polyvinyl ester or polyvinyl acetal layer which contains a compound capable of diffusing and altering properties of a silver image and is hydrolyzable, and upon hydrolysis, becomes permeable to an alkali, and (2) a regenerated cellulose layer containing silver-precipitating nuclei. As compounds capable of diffusing and altering the properties of a silver image, organic mercapto compounds are described.
Furthermore, Japanese Patent Publication No. 21140/81 and International patent application WO No. 2332/80 disclose a method of preventing the fading of a silver image by causing noble metal compounds to act on the silver image.
It has been found, however, that the organic mercapto compounds and noble metal compounds cause various problems such as staining and adverse influences on the image-forming speed because they must be added in a large amount for the protection of a silver image.
Under such circumstances, an improved photographic element for the silver salt diffusion transfer method, using a silver halide emulsion layer containing at least silver iodide as a light-sensitive layer has been proposed (U.S. patent application Ser. No. 821,198, filed Jan. 22, 1986, which corresponds to Japanese Patent Application No. 9344/85), in which the image-receiving element is provided with an iodine ion-capturing layer which is sandwiched between a support and an image-receiving layer on the support, the image-receiving layer contains silver-precipitating nuclei.
In practice, however, it has been found that several problems are encountered in incorporating the iodine ion-capturing layer. One of the problems is that the adhesion between adjacent layers is poor and the layers readily separate from each other. Another unexpected problem is that the coating is poor in flexibility; when cut or bent, the coating readily cracks.